Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.46   11.143%   $262.8087   $262.81   $262.80   $262.80  
  Purchase #2 $122.82   12.464%   $138.1283   $138.13   $138.15   $138.10  
  Purchase #3 $138.65   11.182%   $154.1538   $154.15   $154.15   $154.20  
  Purchase #4 $198.82   5.871%   $210.4927   $210.49   $210.50   $210.50  
  Purchase #5 $56.32   12.342%   $63.271   $63.27   $63.25   $63.30  
  Purchase #6 $39.81   8.337%   $43.129   $43.13   $43.15   $43.10  
  Purchase #7 $50.98   7.484%   $54.7953   $54.80   $54.80   $54.80  
  7 purchase totals = $843.86       $926.7788   $926.78   $926.80   $926.80